Liquid crystal display having passivation layer partially exposing gate insulating layer

ABSTRACT

A method of removing pattern defects in a liquid crystal display more particularly, a liquid crystal display having an IOP structure where a transparent conductive layer is formed on a passivation layer, removes pattern defects in active layers or data wires of an LCD simultaneously and quickly, without causing any damage on other parts of the LCD, by exposing pattern defects in the air, then carrying out an etching process in use of pixel electrodes and an etch-stop layer as an etch mask. The method of removing pattern defects in a liquid crystal display, wherein the liquid crystal display comprises a gate wire on a substrate wherein the gate wire includes a gate electrode and gate line, a gate insulating layer covering an exposed surface of the substrate including the gate wire, a data wire on the gate insulating layer wherein the data wire includes a data line, source electrode, and drain electrode, an active layer on the gate insulating layer wherein the active layer constitutes a thin film transistor with the gate, source, and drain electrodes which are properly overlapped one another, a passivation layer covering an exposed surface of the substrate except a portion of the data wire, and a pixel electrode on the passivation layer wherein the pixel electrode is connected to the exposed data wire, includes the steps of forming an etch-stop layer covering the data wire and thin film transistor, exposing at least one pattern defect by etching the passivation layer in use of the etch-stop layer and pixel electrode as an etch mask, removing the pattern defect, and removing the etch-stop layer.

This application is a continuation of prior application Ser. No.09/468,354, filed Dec. 21, 1999 now U.S. Pat. No. 6,624,871.

This application claims the benefit of Korean Patent Application No.1999-3887, filed on Feb. 5, 1999, which is hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display and a methodof removing pattern defects thereof, more particularly, to a method ofremoving pattern defects (poor patterns) of a liquid crystal displayhaving an IOP structure, where a transparent conductive layer is formedon a passivation layer.

2. Description of the Related Art

Data lines or active layers for liquid crystal display (hereinafterabbreviated LCD) are formed by depositing a conductive or semiconductorlayer on an exposed surface of a substrate, then etching the depositedlayer by photolithography. Residue may remain at an unwanted place ifthe layer is not properly patterned during photolithography. The residueof the conductive or semiconductor layer remaining as pattern defects(poor patterns) on the substrate may cause an electrical malfunction ofthe LCD. Therefore, an LCD in which pattern defects are removed afterfabrication is typically used as a final product. Otherwise, LCDs whichare unrepairable are wasted.

FIG. 1 shows a layout for explaining a method of removing patterndefects in an LCD according to a related art, and FIG. 2 is across-sectional view of the LCD bisected along with the cutting line I—Iin FIG. 1.

Referring to FIG. 1 and FIG. 2, a plurality of pixel cells are definedby the places where gate lines 11L and data lines 15L cross each other.A thin film transistor (hereinafter abbreviated TFT) and a pixelelectrode 17 are formed in each pixel cell. A data signal transmittedthrough the data line 15L is transferred to the pixel electrode 17 byswitching characteristics of TFT.

As shown in FIG. 2, a gate wire, including a gate electrode 11G and agate line 11L, is formed on a substrate 100, and a gate insulating layer12 covers an exposed surface of the substrate including the gate wire.An active layer 13, which follows along with the data line 15L, isformed on the gate insulating layer 12 over the gate electrode 11G.

A data wire is formed over the substrate including the active layer 13.The data wire consists of: the data line 15L crossing the gate line 11Lto define a plurality of pixel cells; a source electrode 15S protrudingout from the data line 15L; a drain electrode 15D standing face to faceopposite the source electrode 15S, and a data pad 15P at the end of thedata line 15L.

A passivation layer 16 covers an exposed surface of the structure,except for portions of the drain electrode 15D and data pad 15P. A pixelelectrode 17 connected to the drain electrode 15D and a data coveringlayer 17P covering the data pad 15P are formed on the passivation layer16.

In the above-structured LCD, pattern defects 101 and 102 may begenerated, for example, when a portion of the active layer or data wirepattern remains at the site between the data line 15L and pixelelectrode 17, or the space between the data pads 15P.

Remaining unwanted locations of electrically-conductive pattern defectsgenerated from the active layer or data wire may degrade or impair theelectrical function or performance of the LCD. Therefore, a process forremoving the pattern defects is necessary.

One method of the related arts of removing pattern defects, is toirradiate a laser beam on a predetermined portion of the device. Forinstance, as shown in FIG. 2, an LCD is repaired by irradiating laserbeams to the pattern defects 101 and 102 to be cut selectively. Namely,the passivation layer 16 and pattern defects 101 and 102 are removed bybeing irradiated by laser beams.

The method of removing pattern defects in an LCD according to therelated art which uses laser, beams is effective provided that thepattern defects exist locally. Unfortunately, the related art is lesseffective when the sizes of the pattern defects are large, or when thepattern defects are distributed over a relatively large area and variousplaces, because it takes a long time to remove them individually bylaser beams. Moreover, wires near the pattern defects are damaged, whenpinpoint laser irradiation is not expected, as each pattern defect mustbe irradiated by each laser beam.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a liquid crystaldisplay, and a method of removing pattern defects thereof, thatsubstantially obviates one or more of the problems due to limitationsand disadvantages of the related art.

An object of the present invention is to provide a liquid crystaldisplay and a method of removing pattern defects thereof which removespattern defects in active layers or data wires of an LCD simultaneouslyand quickly, without causing any damage to other parts of the LCD.According to the invention, this object may be accomplished by exposingpattern defects in the air, then by carrying out an etching processusing pixel electrodes and an etch-stop layer as an etch mask.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, the presentinvention provides a method of removing pattern defects in a liquidcrystal display, wherein the liquid crystal display comprises; a gatewire on a substrate, the gate wire including a gate electrode and gateline; a gate insulating layer covering an exposed surface of thesubstrate including the gate wire; a data wire on the gate insulatinglayer, the data wire including a data line, source electrode, and drainelectrode; an active layer on the gate insulating layer, the activelayer constituting a thin film transistor with gate, source, and drainelectrodes which properly overlap one another; a passivation layercovering an exposed surface of the substrate except a portion of thedata wire; and a pixel electrode on the passivation layer wherein thepixel electrode is connected to the exposed data wire. The methodincludes the steps of forming an etch-stop layer covering the data wireand thin film transistor, exposing at least one pattern defect byetching the passivation layer, using the etch-stop layer and pixelelectrode as an etch mask, removing the pattern defect, and removing theetch-stop layer. The etch-stop layer also may be extended to cover thepixel electrode.

In another aspect, the present invention includes: a substrate; a gatewire on the substrate, the gate wire including a gate electrode and gateline; a gate insulating layer covering an exposed surface of thesubstrate, including the gate wire; a data wire on the gate insulatinglayer, the data wire including a data line, source electrode, and drainelectrode; a thin film transistor connected electrically to the dataline on the gate insulating layer, the thin film transistor including anactive layer constituting a thin film transistor with gate, source, anddrain electrodes which properly overlap one another; a pixel electrodeconnected to the drain electrode of the thin film transistor; and apassivation layer covering the data wire and thin film transistor exceptthe drain electrode, wherein the passivation layer is covered by thepixel electrode and exposes the gate insulating layer except portions ofthe gate insulating layer where the data wire, thin film transistor, andpixel electrode are formed.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

In the drawings:

FIG. 1 shows a layout for explaining a method of removing patterndefects in LCD according to a related art;

FIG. 2 is a cross-sectional view of the LCD of FIG. 1 bisected alongwith the cutting line I—I;

FIG. 3 shows a layout for explaining a method of removing patterndefects in an LCD according to a first embodiment of the presentinvention;

FIG. 4A to FIG. 4C show cross-sectional views bisected along with thecutting line II—II in FIG. 3, for explaining a method of removingpattern defects in an LCD;

FIG. 5 shows a layout for explaining a method of removing patterndefects in LCD according to a second embodiment of the presentinvention;

FIG. 6A to FIG. 6C show cross-sectional views bisected along with thecutting line III—III in FIG. 5 for explaining a method of removingpattern defects in an LCD; and

FIG. 7 shows a cross-sectional view of an LCD according to a thirdembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiment of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

FIG. 3 shows a layout for explaining a method of removing patterndefects in LCD according to a first embodiment of the present invention,and FIG. 4A to FIG. 4C show cross-sectional views bisected along withthe cutting line II—II in FIG. 3 for illustrating a process of removingpattern defects in an LCD wherein the steps of removing pattern defectsare shown in order.

In the following description of the embodiment, a transparent conductivelayer lies on a passivation layer, which is a so-called IOP structure,and an active layer pattern follows a data line.

Referring to FIG. 3, a plurality of pixel cells are defined by gatelines 31L and data lines 35L, which cross one another. A TFT and a pixelelectrode 37 are formed in each pixel cell, and a data signaltransmitted through the data line 35L is transferred to the pixelelectrode 37 by switching characteristics of the TFT.

As shown in FIG. 4A, a gate wire, including a gate electrode 31G and agate line 31L, is formed on a substrate 300, and a gate insulating layer32 covers an exposed surface of the substrate including the gate wire.In this case, a gate wire of at least one layer may be formed.

When a double-layered gate wire is formed, the first layer is formed ofA1, which has excellent electrical conductivity, and the second layer isformed of a conventional metal, such as Mo, Cr, Ta and the like.

An active layer 33, which follows along with the data line 35L, isformed on the gate insulating layer 32 over the gate electrode 31G.

A data wire is formed over the substrate including the active layer 33.The data wire consists of the data line 35L crossing with the gate line31L to define a plurality of pixel cells, a source electrode 35Sprotruding out from the data line 35L, a drain electrode 35D standingface to face opposite the source electrode 35S, and a data pad 35P atthe end of the data line 35L.

In this case, the data wire, which comprises of the source electrode35S, drain electrode 35D, data pad 35P, and data line 35L, of at leastone layer may be formed. When a double-layered data wire is formed, thefirst layer is formed of A1, which has excellent electricalconductivity, and the second layer is formed of a conventional metal,such as Mo, Cr, Ta and the like. An ohmic contact layer 34 made of asemiconductor layer doped with impurities may be formed at an interfacebetween the data wire and the active layer 33 to improve contactresistance.

A passivation layer 36 covers an exposed surface of the structure,except for the drain electrode 35D and data pad 35P. A pixel electrode37 connected to the drain electrode 35D, and a data wire covering layer37P covering the data pad 35P, are formed on the passivation layer 36.The data wire covering layer 37P may be formed of a transparentconductive substance used for the pixel electrode 37.

In the above-structured LCD, pattern defects may be generated as aportion of the active layer or data wire pattern remains at the areabetween the data line 35L and pixel electrode 37, or the space betweenthe data pads 35P (i.e. between the wires). The pattern defects 301 and302 are marked on the layout and cross-sectional views.

The active layer pattern defect may be formed when a semiconductor layerhaving been formed on the gate insulating layer 32 is etched byphotolithography. And, the data wire pattern defect may be formed when aconductive layer having been deposited for a data wire on the gateinsulating layer 32 and active layer 33 is patterned byphotolithography. Remaining unwanted locations ofelectrically-conductive pattern defects generated from the active layeror data wire may degrade or impair the electrical function ofperformance of the LCD. Therefore, a process for removing the patterndefects is required.

The present invention provides a technique which removes the activelayer and/or data wire pattern defects simultaneously, by forming anetch-stop layer 39 which covers the wires of the LCD having thestructure of the related art, exposing the pattern defects 302 and 303on the gate insulating layer 32 in the air by etching the passivationlayer, using the etch-stop layer 39 as an etch mask, then removing thepattern defects by carrying out an etching process.

FIG. 4A to FIG. 4C show cross-sectional views bisected along with thecutting line II—II in FIG. 3 for illustrating a process of removingpattern defects in LCD.

Referring to FIG. 4A, a photoresist pattern 39 is formed over an exposedsurface of a substrate 300. The photoresist pattern 39 is formed tocover a data wire and a TFT. Namely, the photoresist pattern is formedto fully cover a data line 35L, source electrode 35S, drain electrode35D, a channel region 33C, and data covering layer 37P. An overallfigure of the photoresist pattern 39 is well shown in the layout of FIG.3. The photoresist pattern 39 does not cover the pattern defect 301which may exist between the data line 35L and pixel electrode 37 or/andthe other pattern defect 302 which may exist between the data pads 35P.

Referring to FIG. 4B, an exposed portion of the passivation layer 36 isetched away by an etchant such as an etching gas or an etching solutionwhich can etch the passivation layer. When the passivation layer 36 ismade of silicon nitride, the etchant is preferably one of mixed gasesand solutions, such as SF₆+O₂/He, C₂F₆+O₂, ammonium fluoride/HF, and thelike for dry or wet etch.

In this case, the pixel electrode 37 made of ITO (Indium Tin Oxide) haslow etch selectivity against the etchant which etches the passivationlayer 36, working as an etch-stopping layer. Thus, a portion of thepassivation layer 36 which is not protected by the photoresist pattern39 and pixel electrode 37 is removed to expose the pattern defects 301and 302 on the gate insulating layer 32. Etching conditions are properlyadjusted so as not to remove the gate insulating layer 32 while etchingthe passivation layer around the gate line 31L. Portions of the gateline 31L may be damaged in the following process if the gate insulatinglayer 32 near the gate line 31L is etched.

Referring to FIG. 4C, the exposed pattern defects are removed by aproper etching gas or solution. When the pattern defects are made of asubstance used to form the active layer or data wire, an etchant whichhas a high etch selectivity to each of them is used for removal. Thepresent invention by using an etch process, enables the removal of anumber of pattern defects in short time, compared to the related art ofusing laser beams. Finally, the photoresist pattern is removed, and thesubstrate of a TFT LCD is prepared.

As the photoresist pattern 39 fully covers the data wire and TFT fully,the following benefits are provided. The channel region 33 is protected,since the TFT element is fully covered by the photoresist pattern 39.And, leakage current generated between the data line 35L and pixelelectrode 37 due to particles produced from subsequent processes arereduced. Moreover, ‘lift-off’ of the pixel electrode 37 or data coveringlayer 37P due to the undercut at respective steps is prevented duringthe removal of the pattern defects by having the step parts between thesource and drain electrodes 35S and 35D, the active layer 33, and thedata pad 35P fully covered by the photoresist pattern 39.

FIG. 5 shows a layout for explaining a method of removing patterndefects in LCD according to a second embodiment, wherein the LCDincludes on-gate storage capacitors. The LCD shown here has the IOPstructure in which a transparent conductive layer lies on a passivationlayer. Also, the layout shows an active layer lies along with the dataline.

Referring to FIG. 5, a thin film transistor is constituted where thegate and data lines 51L and 55L respectively cross each other. The TFTcomprises a source electrode 51S, a gate electrode 51G which is aportion of the gate line 51L, a drain electrode 55D standing face toface opposite the source electrode 51S, and an active layer 53overlapped with these electrodes. The drain electrode 55D is connectedto a first pixel electrode 57.

The gate line 51L selectively overlaps a second pixel electrode 67 inthe neighboring stage, forming an on-gate storage capacitor. As the gateline 51L is unable to sufficiently overlap the second pixel electrode67, in this case, a subsidiary electrode 55A connected to the secondpixel electrode 67 is formed over the pixel electrode 67 to beoverlapped by the gate line 51L. Therefore, the storage capacitance isincreased to be proportional to the amount of area that the gate line51L overlaps the subsidiary electrode 55A.

Reference the numeral 59 indicates an etch-stop layer which covers thedata line 55L and TFT element completely.

The second embodiment provides a technique which removes the patterndefect 501 such as the active layer and/or data wire pattern defectssimultaneously, by forming an etch-stop layer 59 which covers the datawire (including the data line 55L and subsidiary electrode 55A) of theLCD by exposing the pattern defect 501 on the gate insulating layer,using the air by etching the passivation layer, using the etch-stoplayer 59 as an etch mask, then removing the pattern defects by carryingout an etching process.

FIG. 6A to FIG. 6C show cross-sectional views bisected along with thecutting line III—III in FIG. 5 illustrating a process for removingdefects in an LCD. The cross-sectional views illustrate only part of thestructure of a conventional IOP typed LCD.

Referring to FIG. 6A, a photoresist pattern 59 is formed over an exposedsurface of a substrate 500. The photoresist pattern 59 is formed tocover a data wire including a data line, 55L TFT, and subsidiaryelectrode 55A. An overall figure of the photoresist pattern 59 is wellshown in a layout of FIG. 5. The photoresist pattern 59 exposes thepattern defect 501 existing at the space between the data line 55L andpixel electrode 57 or/and between the subsidiary electrode 55A and pixelelectrode 57 so as not to block the pattern defect 501.

Referring to FIG. 6B, an exposed portion of the passivation layer 56 isetched away by an etchant, such as an etching gas or an etchingsolution, which can etch the passivation layer 56. When the passivationlayer 56 is made of silicon nitride, the etchant is preferably one ofmixed gases or solutions such as SF₆+O₂/He or C₂F₆+O₂, ammoniumfluoride/HF, and the like, for dry or wet etch.

The pixel electrode 57 made of ITO (Indium Tin Oxide) has low etchselectivity against the etchant which etches the passivation layer 56,working as an etch-stopping layer. Thus, a portion of the passivationlayer 56 which is not protected by the photoresist pattern 59 and pixelelectrodes 57 and 67 is removed to expose the pattern defects 501 on thegate insulating layer 52.

The etching conditions are properly adjusted so as not to remove thegate insulating layer 52 while etching the passivation layer around thegate line 51L. Portions of the gate line 51L may be damaged in thefollowing process if the gate insulating layer 52 near the gate line 51Lis etched.

Referring to FIG. 6C, the exposed pattern defect is removed by properetching gases or solutions. When the pattern defect is made of asubstance used to form the active layer or data wire, an etchant whichhas a high etch selectivity to each of them is used for removal.

Finally, the etch-stop layer is removed.

The second embodiment enables the removal of a number of pattern defectsquickly, compared to the related art of using laser beams, by using anetch process.

The first and second embodiments provide an etch-stop layer to cover thedata line/TFT element, or the data wire element such as the subsidiaryelectrode of a storage capacitor, as examples. In this case, the pixelelectrode works as additional etch-stop layer during the process ofetching the passivation layer.

However, in some cases a new etch-stop layer may be needed because aportion of the pixel electrode may be damaged by the etchant, or“lift-off” may occur due to over-etch under the pixel electrode. Thus, athird embodiment of the present invention will meet that need.

FIG. 7 shows a cross-sectional view illustrating a method of an LCDaccording to a third embodiment, wherein an etch-stop layer is formedsufficient to cover a pixel electrode. The drawing illustrates the LCDstructure as in the first embodiment, to explain the third embodiment,and the same numerals designate the same elements in the drawings.

The third embodiment is different from the first in that an etch-stoplayer 49 covers pixel electrodes 37 and 47 as well as the data line andTFT element. Compared to first and second embodiments, the thirdembodiment has the advantage that a passivation layer 36 beneath thepixel electrodes 37 and 47 is protected when the pattern defects 301 and302 are exposed to be removed. Namely, “lift-off” of the pixelelectrodes due to over-etch of the passivation layer is prevented as thepassivation layer is etched, using the etch-stop layer 49, which iswider than the pixel electrodes, as an etch mask. According to anothertechnique, the pattern defects are removed by forming an etch-stop layerwhich covers all wires in an LCD except the sites between wires, byetching a passivation layer which is hot covered by the etch-stop layerto expose the pattern defects, then by removing the pattern defects.According to still another technique, the pattern defects are removed byexposing the pattern defects by etching a passivation layer selectively,then by etching the pattern defects away.

Accordingly, pattern defects which exist widely as well as locally, arequickly removed, thereby increasing productivity. Moreover, patterndefects are removed without causing any damage on other parts of theLCD, as the parts necessary for operating the LCD are covered by apassivation layer during the etching process of removing the patterndefects.

It will be apparent to those skilled in the art that variousmodifications and variation can be made in the liquid crystal displayand method of removing pattern defects thereof of the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A liquid crystal display comprising: a substrate; a gate wire on thesubstrate, the gate wire including a gate electrode and gate line; agate insulating layer covering an exposed surface of the substrateincluding the gate wire; a thin film transistor formed in an activelayer on the gate insulating layer, the thin film transistor having thegate electrode and further having a source electrode and a drainelectrode; a data wire on the gate insulating layer, the data wireincluding a data line, the source electrode, and the drain electrode; apixel electrode connected to the drain electrode of the thin filmtransistor; and a passivation layer covering the data wire and the thinfilm transistor, except the drain electrode, the passivation layer beingcovered by the pixel electrode, the passivation layer exposing the gateinsulating layer except portions of the gate insulating layer where thedata wire, the thin film transistor, and pixel electrode are formed; adata pad at an end of the data line, said data pad being covered withthe passivation layer; a contact hole in the passivation layer, thecontact hole exposing an exposed portion of the data pad; and a data padcovering layer covering the exposed portion of the data pad.
 2. Theliquid crystal display according to claim 1, wherein a part of the datawire on the gate insulating layer over the gate line comprises asubsidiary electrode, and wherein the subsidiary electrode comprises anexposed portion and a remainder portion being covered with thepassivation layer, and wherein the exposed portion of the subsidiaryelectrode is connected to a pixel electrode.
 3. The liquid crystaldisplay according to claim 1, wherein the passivation layer covers thedata wire and thin film transistor, and exposes a portion of the pixelelectrode.